The band was set to headline the four-day festival on May 9, but plans changed after Weir reportedly fell onstage during a recent performance in Port Chester, New York. He was unable to finish that concert, according to reports.

Furthur made an announcement on its website that it was canceling the BottleRock appearance:

"Due to unforeseen circumstances, Furthur regretfully will be unable to appear as scheduled at BottleRock Napa Valley on Thursday, May 9. Grateful Dead and Furthur co-founder Bob Weir is unable to perform in any capacity for the next several weeks.

FILE - This May 9, 2009 file photo shows Phil Lesh, left on bass, with Bob Weir, center and Warren Haynes, right, performing with their band The Dead, formerly the Grateful Dead at the Forum in the Inglewood section of Los Angeles, Calif. Weir fell onstage while strumming his guitar at a concert in Port Chester, N.Y. In a video posted online, the 65-year-old musician collapsed Thursday during a performance with his Furthur bandmates at The Capitol Theatre. He was quickly helped off the floor as the crowd cheered him on. Weir is currently on a tour with Furthur, the band he formed with fellow Grateful Dead bandmate Phil Lesh. Lesh told the crowd Thursday that Weir had been suffering from a strained shoulder. (AP Photo/Richard Vogel, file) (Ricahrd Vogel)

"Furthur featuring Phil Lesh and Bob Weir look forward to returning to the road as scheduled on July 11 in Brooklyn for their summer tour, which carries them through early October on the West Coast."

While the loss is a major hit for the inaugural BottleRock festival, which runs May 9-12 in downtown Napa, the festival still has many other big-time headliners, including the Black Keys and the Zac Brown Band. For more information, visit http://bottlerocknapavalley.com.